Dispensing systems for supplying liquid material and filaments in other forms are conventionally used to apply thermoplastic materials, such as hot melt adhesives, to various substrates during the manufacture of diapers, sanitary napkins, surgical drapes, and other substrates. Typically, liquid material and pressurized air are supplied to the dispenser where they are heated and distributed to one or more dispensing modules for application to the substrate. The heated liquid material is discharged from the dispensing module while pressurized air is directed toward the dispensed liquid to attenuate or draw down the dispensed liquid material and to control the pattern of the liquid material as it is applied to the substrate.
Conventionally, liquid material dispensing systems have utilized separate manifolds for heating and supplying the pressurized air and liquid material to the dispensing modules. Accordingly, the separate air and liquid material manifolds use separate heaters specifically dedicated to heat the respective air and liquid material. Generally, the requirements for heating the liquid and air are different, therefore, different types of heating elements are typically used for each heater and the heating elements are separately controlled. This in turn contributes to increased manufacturing costs and the need to stock multiple service parts. Having separate air and liquid material manifolds also inhibits making the dispensers compact in size. Because the air and liquid material heaters are separately controlled, heat generated from one heater can interfere with the temperature control of the other material. For example, the heater for heating the air may be turned off by a controller in an effort to reduce the temperature of the pressurized air, but heat generated by the liquid material heater may continue to heat the air, thereby effectively contravening efforts to control the air temperature with the air heater. Finally, a dispenser having separate manifolds increases manufacturing time due to the need to couple together the individual manifolds to produce the adhesive dispenser.
Adhesive dispensing systems generally have manifolds configured to accommodate a fixed number of adhesive dispensing modules. Often, however, it is desirable to have an adhesive dispenser of a modular configuration which permits manifolds of the dispenser to be joined together or separated to permit flexibility in increasing or decreasing the number of modules which can be used in a given application. Such modular adhesive dispensers present unique challenges such as maintaining uniform heating across all modules so that liquid material is uniformly dispensed to the substrate, particularly from dispensing modules located at the ends of each manifold where less heat from the manifold heaters is transferred to the liquid material due to heat losses through the ends of the manifold.
A need therefore exists for an improved liquid material dispensing system which addresses various drawbacks of prior dispensing systems, such as those described above.